View on the Robinson Crusoe Island on of the Juan Fernandez islands, Chile. Photograph: Schmitz-Söhnigen/Corbis

To call my recent reading of Robinson Crusoe a rereading is stretching the truth, because I don't think I have read the whole novel before. As soon as I was able to read by myself, I tried and failed to finish it, as I did Gulliver's Travels, because both had been waiting on my bookshelf, along with Peter Pan, Alice's Adventures in Wonderland, The Wizard of Oz, The Lion, the Witch and the Wardrobe and Treasure Island. My books were a kind of job-lot of essential reading for children bought for me at birth by my parents, who were not literary, but had high ambitions for their newborn.

Faraway and imaginary places, Neverland, Wonderland, Oz, Narnia and Captain Flint's island seem to belong to the world of children, which is how, I suppose, Lilliput and the uninhabited island "on the Coast of America, near the Mouth of the Great River of Oroonoque" on which Robinson Crusoe was shipwrecked for 28 years came to be included. All the other books I read obsessively, disappeared into them even, but Swift and Defoe's stories of the adventures of Lemuel Gulliver and Robinson Crusoe simply bored me.

I hated the idea that there were books I couldn't read - like secrets I couldn't be told - so I tried repeatedly, but always failed to get very far. Perhaps it was the 18th-century language - though I imagine they were edited children's editions - but having at last, five decades later, read Robinson Crusoe, I suspect that what I most disliked then was the dogged, repetitive, unrelenting detail of Crusoe's struggle for existence, which is now precisely what I find myself relishing, so much so that when I finished Defoe's intensely readable book last year, I immediately started all over again.

The castaway Robinson Crusoe, who makes a life for himself in an alien world, may be the Wizard of Oz, but he is not Prospero. There is no magic on his island, only the increasingly agreeable reality which with sheer slog he manages to provide for himself. Crusoe rebuilds a simple version of the world he once knew in the island wilderness in which he finds himself. Not from nothing at all, as God created the world, but luckily - as in a computer game - there are handy objects available. Visiting his wrecked ship offshore he finds enough basic necessities to sustain his life - some grain to plant, a hatchet, rope, muskets and gunpowder.

It seems very pedestrian, but as I read this time, I grew aware of the wonderful game Defoe plays with time, and the powerful role of dark imagination in his hero's survival. After his initial despair, what forces Crusoe to begin making a life for himself is fear. Imagining the worst always, picturing fearsome wild animals and flesh-hungry cannibals, he finds himself a cave and constructs an impenetrable defensive wall around it. It is only some time later that we're told it took years to complete it. Then he plants some grain, but several seasons pass before he has worked out when best to sow it, and years go by before he has enough corn to spare to make bread with it. Even then he has to invent the means to prepare the flour and bake the dough.

Defoe guides his reader towards a vivid understanding of the terrible lack of hurry in Crusoe's world. After Crusoe has spent more than 50 pages describing retrospectively how everything was done, he presents the journal he kept, which describes in even more detail, day by day, what we have just been told. Time slows down. Meticulous detail and repetition beat a slow tattoo of endless time.

Not boring, it turns out, if you allow yourself to read for rhythm, but hypnotic. When Crusoe describes making a plank of wood, using an entire tree for a single board and whittling it away for months with a hatchet until it finally serves its purpose as a shelf or a table top, it is as if we are watching the aeons it took humankind to develop towards civilisation. By painful degrees, Crusoe learns to make shelter, hunt, start to cultivate the land, begin to domesticate the wild goats, explore the island, and even manage eventually to make himself that ultimate of civilised acquisitions, a second home: a country estate, as he calls it, in the idyllic middle of the island.

As he builds his material world with his own hands, Crusoe, the plantation owner on his way to buy slaves when he was shipwrecked, discovers the fundamental truth of economics: without society, surplus is waste not profit. Only what he can use has value.

Defoe also has Crusoe proceed toward the spiritual (or, it may be, superstitious) life of humanity, and convert from a thoughtless, wayward young man who had no interest in the meaning of his existence, to one who understands the need the vulnerable have for a personal god. Still, he remains a pragmatic convert. God's providence is a comforting notion, but he knows better than to rely on it. Whenever real dangers appear, he finds a real solution. Only later does he thank God for his salvation. And the mysterious single footprint he sees in the sand - not a pair, just the one - is both a real and imaginary horror that sends him into hiding for years.

Yet, once his worst fears are confirmed, that there are indeed cannibals who drop by to eat their captives, he learns to live with their reality. Keeping to his side of the island, he overcomes his western revulsion at another culture, to arrive at the decision not to judge the ways of the other.

He conceives of himself as king of his empty island, but it is not until he rescues Friday from the cannibals, 23 years on, that he has any subjects. Then he learns (patronisingly, it is true) to love his sole companion and wonders how it has come about that all men are not treated as equals. Of course, he returns to the 18th century a rich man, and Friday, after a gothic adventure or two, disappears from sight. But there is a sense that it is possible for people to learn. All they need, apparently, is 23 years of total isolation.

· Jenny Diski's latest novel is After These Things, published by Little, Brown, price £14.99